The defense is a work-in-progress, but it's definitely head and shoulders above where it was a year ago (since, a year ago, the defense was basically Junior-B level).
What i'm a little worried about is secondary scoring. The Oilers seem to have good depth at forward, with three lines that can potentially score, but 'potential' doesn't mean "will". If lines 2 and 3 do dry up even for a few weeks, the losses could pile up, especially since there's (apparently) still no offensive help from the blue line.
I could foresee a lot of games like the Vancouver game the other day, where the McDavid line does its job, but the team still loses 3-2 to a not-so-great-teams because nobody else scored.
I think the key is either the RNH-line or Draisaitl-line needs to step up and really have a big season to support the top line. If they don't, Chiarelli's gonna have to figure out a way to get a D-man on the power-play who can actually score or put pucks on net.
With no secondary scoring and no blue-line help on the power-play, the team is going nowhere.